This invention relates to graphic articles and in particular retroreflective graphic articles and to methods for making the articles by electrographic printing means.
A variety of print methods have been employed for imaging various sheet materials. Commonly employed print methods include gravure, off-set, flexographic, lithographic, electrographic (including electrostatic), electrophotographic (including laser printing and xerography), ion deposition (also referred to as electron beam imaging [EBI]), magnetographics, ink jet printing, screen printing and thermal mass transfer.
Electrostatic printing consists of an imaging step that involves direct deposition of electrostatic charge onto a surface that has been prepared to be printed followed by the toning step using liquid toners. This is followed by a step that involves fusing the toners with heat and/or pressure. Printers using this technology are available in wide widths up to 52 inches and are used for printing architectural drawings, billboards, etc. Thermal mass transfer printing uses computer-generated digital text and graphics data to drive a thermal printhead that melts spots of ink on doner ribbons and transfers them to a receiver. Systems in use have built-in computers and produce finished labels and other printed products with over 25% variable information in 4 colors laminated and either rotary or flat die-cut.
One of ordinary skill in the art appreciates the differences in these various print methods and recognizes that receptor sheets are typically not interchangeable such that high image quality results regardless of the printing method.
The present invention provides a method for making a base construction useful for making a retroreflective graphic article therefrom. Accordingly, the present invention in its first aspect is a method for making a base construction suitable for use in making a retroreflective article comprising the steps of electrographically printing an image on an image transfer sheet and contacting the image on the image transfer sheet to a base material under pressure and at an elevated temperature so that the image is transferred to a surface of the base material wherein the surface of the base material comprises a binder layer of polyvinyl butyral resin having glass microspheres enclosed therein and a specular reflective layer underlying and spaced apart from the microspheres by the resin.
A second aspect of the present invention further comprises the step of scanning an image to a computer to store the image in an electronic form wherein the stored image is electrographically printed on the image transfer sheet.
A third aspect of the present invention further comprises the step of applying a clear film to the surface of the base material having the transferred image thereon to provide a retroreflective graphic article.
In a fourth aspect of the invention, the retroreflective base material is affixed to a removable liner by a pressure sensitive adhesive layer and the printed image is applied to the side of the retroreflective base material opposite the side having the removable liner and adhesive layer. In a further aspect of the invention, the liner is removed from the pressure sensitive adhesive layer after forming a retroreflective article and the article is adhered to a substrate.
In another embodiment, the present invention is a method for making a retroreflective base construction comprising the steps of electrographically printing an image on an image transfer sheet and contacting the image on the image transfer sheet to a base material under pressure and at an elevated temperature so that the image is transferred to a surface of the base material wherein the surface of the base material comprises a binder layer selected from aliphatic polyurethane and polyurethane extended polyethylene terephthalate polymers having glass microspheres enclosed therein and a specular reflective layer underlying and spaced apart from the microspheres by the resin and applying a clear film to the surface of the base material having the transferred image.
In further aspects, the invention comprises the retroreflective base construction and retroreflective articles made according to the above described processes.